Re: [PATCH] block: fix splitting segments

[Ming Lei <ming.lei@redhat.com>]

On Tue, Jan 07, 2020 at 04:47:08AM -0800, Guenter Roeck wrote:
> Hi,
> 
> On Sun, Dec 29, 2019 at 10:32:30AM +0800, Ming Lei wrote:
> > There are two issues in get_max_segment_size():
> > 
> > 1) the default segment boudary mask is bypassed, and some devices still
> > require segment to not cross the default 4G boundary
> > 
> > 2) the segment start address isn't taken into account when checking
> > segment boundary limit
> > 
> > Fixes the two issues.
> > 
> > Fixes: dcebd755926b ("block: use bio_for_each_bvec() to compute multi-page bvec count")
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> 
> This patch, pushed into mainline as "block: fix splitting segments on
> boundary masks", results in the following crash when booting 'versatilepb'
> in qemu from disk. Bisect log is attached. Detailed log is at
> https://kerneltests.org/builders/qemu-arm-master/builds/1410/steps/qemubuildcommand/logs/stdio
> 
> Guenter
> 
> ---
> Crash:
> 
> kernel BUG at block/bio.c:1885!
> Internal error: Oops - BUG: 0 [#1] ARM

Please apply the following debug patch, and post the log.

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 347782a24a35..c4aa683a1c20 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -217,6 +217,33 @@ static bool bvec_split_segs(const struct request_queue *q,
 	return len > 0 || bv->bv_len > max_len;
 }
 
+static void blk_dump_bio(struct request_queue *q, struct bio *bio,
+		unsigned secs)
+{
+	struct bvec_iter iter;
+	struct bio_vec bvec;
+	int i = 0;
+	unsigned sectors = 0;
+
+	printk("max_sectors %u max_segs %u max_seg_size %u mask %lx\n",
+			get_max_io_size(q, bio), queue_max_segments(q),
+			queue_max_segment_size(q), queue_segment_boundary(q));
+	printk("%p: %hx/%hx %llu %u, %u\n",
+                       bio,
+                       bio->bi_flags, bio->bi_opf,
+                       (unsigned long long)bio->bi_iter.bi_sector,
+                       bio->bi_iter.bi_size, secs);
+	bio_for_each_bvec(bvec, bio, iter) {
+		sectors += bvec.bv_len >> 9;
+		trace_printk("\t %d: %lu %u %u(%u)\n", i++,
+				(unsigned long)page_to_pfn(bvec.bv_page),
+				bvec.bv_offset,
+				bvec.bv_len, bvec.bv_len >> 12);
+	}
+	printk("\t total sectors %u\n", sectors);
+}
+
+
 /**
  * blk_bio_segment_split - split a bio in two bios
  * @q:    [in] request queue pointer
@@ -273,6 +300,9 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 	return NULL;
 split:
 	*segs = nsegs;
+
+	if (sectors <= 0 || sectors >= bio_sectors(bio))
+		blk_dump_bio(q, bio, sectors);
 	return bio_split(bio, sectors, GFP_NOIO, bs);
 }
 

Thanks,
Ming